Congestive heart failure is accompanied by both abnormal action of aldosterone on the kidney with failure of "escape" from its action as well as abnormally high rates of secretion and plasma aldosterone concentration resulting in excessive sodium and fluid retention. By using a radioimmunoassay technique for aldosterone concentration determination,coupled with control system block analyses and computer solutions, we will analyze the relative influence of the mechanisms controlling plasma aldosterone concentration under both acute and chronic conditions. We will determine the gain of the system, whether it is under open-loop or closed-loop (negative feedback) control, the characteristics of the feedback signal, the sites of the feedback detectors, and the relative importance by using hemodialysis, of sodium depletion as compared with volume depletion in stimulating aldosterone secretion. Bibliographic references: McCaa, R.E., and C.S. McCaa. Aldosterone response in intact conscious dogs to long-term infusion of angiotensin 11 and potassium ions. Clin. Res., 23:13, 1975; Trippodo, N.C., R.E. McCaa, and A.C. Guyton. Effect of prolonged infusion of angiotensin 11 on fluid intake and aldosterone secretion in conscious dogs. Fed. Proc., 34:312, 1975.